The present invention relates to a semiconductor memory device fabricated on a semiconductor substrate, and more particularly to a semiconductor memory device having a redundant array of memory cells.
In order to save a semiconductor memory having a small number of defective memory cells, and to thereby to improve production yields, the redundant technique has been proposed. In the redundant technique, a redundant memory cell array is provided for a normal memory cell array, and a defective memory cell or cells in the normal memory cell array are substituted by good memory cells in the redundant memory cell array. For when substituting the defective memory cell in the normal memory cell array by the good cell in the redundant memory cell array, normal operation address decoders are inhibited when a redundant address decoder selects or designates a good cell in the redundant memory cell array. The above inhibition of operation of the normal address decoders is achieved by applying the selection output signal of the redundant address decoder to the normal address decoders as an inhibition signal. However, the number of the normal address decoders such as row decoders is very large in the recent large capacity semiconductor memory device, and therefore the above selection output must be applied to a large number of address decoders. Therefore, load capacitance of the selection output signal of the redundant address decoder is very large, and therefore the normal address decoders cannot recognize the occurrence of the selection output signal of the redundant address decoder at a high speed but must wait for a certain delay time. Thus, the normal address decoders are controlled to be enabled a predetermined time after the operation of the redundant address decoder. Accordingly, the conventional semiconductor memory device provided with the redundant scheme is not suitable for high speed utilization.